Directional warhead fuze

ABSTRACT

A directional ordnance for a missile. The missile contains circuitry to determine the direction of a target relative to the missile and to selectively detonate directing charges to force the blast from the warhead towards the target. The circuitry for determining the direction of the target includes two transmit antennas, each transmitting a different pseudo noise sequence, and two receive antennas; each coupled to a receiver which can determine the level of each pseudo noise sequence at each receive antenna. The relative strengths of the different pseudo noise sequences tell the direction of the target relative to the transmit and receive antennas.

This invention was made with Government support under Contract No.F08635-88-C-0188, awarded by the Department of the Air Force. TheGovernment has certain rights in this invention.

BACKGROUND OF THE INVENTION

This application relates generally to guided missiles and moreparticularly to improving the effectiveness of missiles fired atairborne targets.

Guided missiles fired at airborne targets are well known. Certain typesof such missiles contain a radar fuzing system. The fuzing systemdetects the presence of a target and measures the range between themissile and the target. At an appropriate range, the fuzing systemdetonates a warhead. The explosion of the warhead propels a cloud ofshrapnel in all directions relative to the missile. If enough of theshrapnel strikes the target at a vulnerable area, the target isdestroyed.

The fuzing system of one existing missile comprises two transmitantennas and two receive antennas. Each transmit antenna radiates aradar signal modulated with a pseudo noise (hereafter PN) sequence intoa roughly 180° sector relative to the missile. Each receive antennareceives radar reflections from a 180° sector. Both transmit antennasare fed the same signal. Likewise, both received signals are combined.Thus, the four antennas provide 360° coverage to both transmit andreceive signals.

The received signal is mixed with several copies of the PN sequence,each delayed by a different time. Mathematically, this mixing correlatesthe received signal with the transmitted signal. The time delayassociated with the delayed copy of the PN signal which produces thehighest correlation indicates the back and forth propagation time to thetarget and, hence, indicates the range to the target. The measured rangeindicates when the fuzing system should detonate the warhead.

To avoid detonating the warhead when no target is present, the warheadis not detonated unless the highest correlation signal exceeds athreshold. The threshold is determined by correlating the PN signal withthe background noise signal present when a reflected radar signal is notbeing received. This threshold signal gives a measure of the backgroundnoise level. Accordingly, the warhead is not detonated unless thehighest correlation signal is above the noise.

While this arrangement for detonating a warhead is adequate for someapplications, it is desirable to improve the effectiveness of themissile for other applications.

One way to improve the effectiveness of a missile is to direct theenergy from the detonation of the warhead towards the target.Directional warheads are known that contain directing charges. In somesystems, called mass focus systems, the directing charge deforms theshell of the missile. When the main explosive charge of the warheadexplodes, the shrapnel tends to be focused towards the deformed region.In other systems, called velocity focus systems, a directing charge isdetonated and creates a shock wave in a particular direction. Theexplosion of the main explosive charge while the shock wave is presentcauses shrapnel in the direction of the shock wave to have a greatervelocity.

Regardless of which type of directional warhead is used, it is necessaryfor the fuze detonating the warhead to determine the direction of thetarget relative to the missile. Additionally, it would be desirable tocreate a directional warhead system with as little change as possible toan existing fuzing system.

SUMMARY OF THE INVENTION

With the foregoing background in mind, it is an object of this inventionto provide a means for improving the effectiveness of a missile byincreasing the amount of energy directed towards the target.

It is also an object of this invention to provide a method of improvingthe effectiveness of a missile while minimizing changes to existingmissile designs.

The foregoing and other objects are achieved by incorporating foursubcharges in the missile warhead. Appropriate ones of the subchargesare detonated within the warhead and the blast from the subchargesdirects shrapnel of increased velocity in the desired direction. Thedesired direction is determined by transmitting, from two transmitantennas, two different PN sequences. The signals received at each oftwo receive antennas are correlated with the two different sequences,thus producing four correlated signals. The relative amplitudes of themaximum values of the correlated signals indicates the direction inwhich the increased velocity, and hence increased energy, shrapnel is tobe directed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the followingmore detailed description and accompanying figures in which

FIG. 1 is a simplified sketch, with a cutaway portion, of a missileincorporating the invention;

FIG. 2 is a sketch of the two-way pattern formed by a combination of onetransmit and one receive antenna;

FIG. 3 is a sketch of the four, two-way patterns formed by combining onetransmit and one receive antenna;

FIG. 4A is a block diagram of the signal processing electronics in themissile of FIG. 1; and

FIG. 4B is a block diagram showing additional details of the analogprocessors in the circuit of FIG. 4A.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a missile 10 fabricated according to the invention. Missile10 is fabricated using known techniques.

As shown, missile 10 has an electronics section 12 which containselectronic circuits to control missile 10. These circuits are fabricatedusing known techniques. For example, electronics section 12 containscircuitry which generates signals to control fins 18 to steer missile10. Electronics section 12 also contains circuitry which detonates mainexplosive charge 14. In addition, electronics section 12 also containscircuitry to simultaneously detonate one or two of the directingexplosive charges 16a-16e. As will be described below, when directingcharge 16e, which runs through the center of main explosive charge 14 isdetonated, the blast produced by main explosive charge 14, will beisotropic. Directing charges 16a-16d can be selectively detonated todirect an increased amount of energy from the blast into one of eightsectors around missile 10.

Electronics section 12 gathers information on the location of a target(not shown) using antennas T₁, R₁, T₂, and R₂. This information allowselectronics section 12 to determine which directing explosive charges tofire and when to fire the charges to direct the maximum amount ofshrapnel with increased energy at the target (not shown). Antennas T₁and T₂ transmit signals which will be described in greater detail below.Antennas R₁ and R₂ receive signals from which electronics section 12calculates the range between missile 10 and the target (not shown) andthe direction of the target relative to missile 10.

The time for firing main explosive charge 14 is determined using knowntechniques. Suffice it to say, the range between missile 10 and thetarget is measured from radar returns from the target. Electronicssection 12 estimates the point of closest approach between missile 10and the target. Main explosive charge 14 is detonated prior to the pointof closest approach. The detonation of main explosive charge 14, as inconventional missiles, creates a cloud of shrapnel around missile 10.

The direction of the target relative to missile 10 is also determined ina manner described below. Electronics section 12 detonates selected oneor ones of the directing explosive charges 16a . . . 16e nearlysimultaneously with detonation of main explosive charge 14. Theexplosive force of the selected ones of directing charges forces thecloud of shrapnel created by the detonation of main explosive charge 14to have an increased velocity toward the target (not shown). Forexample, simultaneous detonation of directing charges 16c and 16bdirects the cloud of shrapnel in the direction labeled Y. Detonation ofdirecting charge 16c directs the cloud of shrapnel in a directionintermediate those labeled X and Y.

Here, four directing charges 16a . . . 16d are shown. These fourdirecting charges can be formed into eight different combinations of oneor two adjacent charges. Thus, electronics section 12 can direct thecloud of shrapnel into one of eight different directions. Thus,electronics section 12 must determine into which of eight sectors aroundmissile 10 the target is located.

The way in which electronics section 12 determines the location of thetarget can be understood by reference to FIGS. 2 and 3. In FIG. 2,missile 10 is shown in cross-section in relation to the axes X and Yshown in FIG. 1.

As in conventional missiles, antennas T₁ and T₂ are connected totransmitters of conventional design (FIG. 4) which produce pseudo noise(hereafter "PN") sequences. Unlike conventional missiles, antennas T₁and T₂ transmit different, independent PN sequences. For convenience,the PN sequences will be denoted Code 1 and Code 2.

Antennas R₁ and R₂ are connected to receivers of conventional design(FIG. 4). In a manner described in greater detail below, each receivedsignal is correlated with both Code 1 and Code 2. As is known, a PNsequence correlated with an identical PN sequence will produce a highoutput at a time indicating the time delay between the PN sequences. APN sequence correlated with a different, independent PN sequence willproduce a uniformly low output. Thus, it can be determined from thesignal received at antennas R₁ or R₂ whether the signal is thereflection of a signal transmitted by antenna T₁ or T₂.

Each of the antennas T₁, T₂, R₁, and R₂ has a coverage pattern ofapproximately 180°. As shown in FIG. 2, antenna pattern 202 roughlyapproximates the angular coverage pattern of transmitting antenna T₁ andantenna pattern 204 roughly approximates the coverage pattern ofreceiving antenna R₁. FIG. 2 shows missile 10 at the origin of acoordinate system. The distance from the origin of any point isproportional to the gain of the antenna pattern in the direction of thatpoint.

As is known, the total antenna gain in any signal path is the product ofthe gain of antenna pattern of the transmit antenna and the antennapattern of the receiving antenna. The product of antenna patterns 202and 204 has a non-zero value in the quadrant denoted Q₁ and is, to arough approximation, zero in quadrants Q₂ . . . Q₄. To a closeapproximation, if the code transmitted by antenna T₁ is received atantenna R₁, then the transmitted signal must have reflected from atarget in quadrant Q₁.

Targets in quadrant Q₂ -Q₄ can be detected in a similar fashion.Reception of Code 1 at antenna R₂ represents reflections from a targetin quadrant Q₂. Reception of Code 2 at antenna R₂ represents reflectionsfrom a target in quadrant Q₃. Reception of Code 2 fat antenna R₂represents reflections from a target in quadrant Q₄. Thus, it can beseen that the transmitted PN sequences (Code 1 and Code 2) can be takenin combination with the signals at the receive antennas to computereflections from a given quadrant. The pair of a PN sequence and areceive antenna thus defines a quadrant.

The actual product of the antenna patterns from antennas T₁ and R₁ doesnot abruptly end at the edges of quadrant Q₁. Rather, two-way coveragepattern 206₁,1 shows a more realistic coverage pattern produced by thecombination of a signal transmitted by antenna T₁ and received byantenna R₁.

To conceptualize one simple way to operate the device, it is useful topicture the space around missile 10 as divided into four quadrants, Q₁,Q₂, Q₃, and Q₄. When a target is detected, its direction relative tomissile 10 is resolved into one of the four quadrants Q₁ . . . Q₄.Selected ones of directing charges 16_(a) . . . 16_(d) could bedetonated to direct the cloud of shrapnel created by main explosivecharge 14 into the appropriate one of the four quadrants.

Further enhancements can be made to remove short-comings of this simpleapproach. It has been found that when a target is near the edge of aquadrant, directing the cloud of shrapnel into the center of thequadrant does not provide the desired efficacy. Accordingly, FIG. 3shows the area around missile 10 divided into eight sectors S₁ . . . S₈.As described above, the cloud of shrapnel created by the detonation ofmain explosive charge 14 can be directed into the center of any of thesesectors by detonating one or two of the directing charges 16a . . . 16d.Thus, electronics section 12 (FIG. 1 ) contains circuitry to process thesignals at antennas R₁ and R₂ to determine in which of the eight sectorsthe target is.

FIG. 3 shows the two-way coverage patterns 206₁,1, 206₁,2, 206₂,2, and206₂,1 created by the various combinations of transmit and receiveantennas. Two-way coverage pattern 206₁,1 is the pattern created byreceiving a signal transmitted by antenna T₁ at antenna R₁. Two-waycoverage pattern 206₁,2 is the pattern created by receiving a signaltransmitted by antenna T₁ at antenna R₂. Two-way coverage pattern 206₂,2is the pattern created by receiving a signal transmitted by antenna T₂at antenna R₂. Two-way coverage pattern 206₂,1 is the pattern created byreceiving a signal transmitted by antenna T₂ at antenna R₁.

It must be recalled that antenna T₁ transmits only Code 1. Thus,coverage patterns 206₁,1 and 206₁,2 are formed by looking at thestrength of the Code 1 signal at antennas R₁ and R₂, respectively.Likewise, coverage patterns 206₂,1 and 206₂,2 are formed by looking atthe strength of the Code 2 signal at antennas R₁ and R₂, respectively.

By comparing the strengths of the two different PN sequences received ateach of antenna R₁ and R₂, it can be determined whether the target (notshown) falls in a direction in which any of the coverage patterns has again significantly above zero.

From the directions of the coverage patterns in which the target falls,the sector in which the target falls can be determined. For example, insector S₃, combined coverage pattern 206₁,2 exceeds both combinedcoverage pattern 206₁,1 and 206₂,2 by a predetermined amount, here 7 dB.Thus, if the strength of the Code 1 signal at antenna R₂ exceeds, by 7dB, the strength of the Code 1 signal at antenna R₂ and the strength ofthe Code 1 signal at antenna R₁, the target is in sector S₁. Directingcharge 16c (FIG. 1) would then be detonated to direct the shrapnel cloudinto the center of sector S₃.

As another example, combined coverage patterns 206₁,1 and 206₁,2 differby less than 7 dB in sector S₂. Thus, if the Code 1 signals at antennasR₁ and R₂ differ by less than 7 dB, directing charges 16b and 16c aredetonated to direct the shrapnel cloud into sector S₂.

Methods for comparing the amplitudes of two signals are well known. Suchan arrangement might include an analog to digital converter (not shown)and a digital processor (not shown). The signals might be compared usinga technique known as amplitude monopulse to accurately determine thedirection of the target relative to missile 10. However, for the presentinvention, it is necessary to resolve the direction of the target intoone of eight sectors around missile 10. Accordingly, a simpler systemcan be used.

FIG. 4A shows a block diagram of a simple system for determining inwhich of the eight sectors S₁ . . . S₈ (FIG. 3) a target falls. Thevarious elements shown in FIG. 4 are well known circuit elements, butthey are configured in a novel fashion.

FIG. 4A shows code generators 406₁ and 406₂. These elements generateCode 1 and Code 2 PN sequences, respectively. Code 1 is passed throughtransmitter 404₁ to antenna T₁, where it is transmitted. Code 2 ispassed through transmitter 404₂ to antenna T₂. As is known, transmitters404₁ and 404₂ amplify and up convert the code signals or modulate acarrier with the code signals.

Portions of the transmitted signals reflected from the target arereceived at antennas R₁ and R₂. The received signals are passed throughreceivers 402₁ and 402₂ to analog processors 412₁,1, 412₁,2, 412₂,1, and412₂,2.

Each of analog processors 412₁,1, 412₁,2, 412₂,1, and 412₂,2 containsidentical circuitry, shown in greater detail in FIG. 4B. Each analogprocessor has two inputs. One input is connected to either codegenerator 406₁ or 406₂. The second input is connected to either receiver402₁ or 402₂. In this way, each of the four pairs of signals that can beformed by selecting one of the two code signals and one of the tworeceived signals is fed to one of the analog processors.

Taking analog processor 412₁,1 as representative, it can be seen thateach analog processor contains a threshold circuit 414, afilter/detection circuit 415, and a correlator 416.

Inside correlator 416, as shown in FIG. 4B, the code signal is brokeninto a plurality, here denoted N+1, of paths. Each path contains one ofthe delay elements 418₀ . . . 418_(N). Each of the delay elements 418₀ .. . 418_(N) has a different delay denoted T₀ . . . T_(N). The length ofthe delays starts at zero for T₀ and increases by the length of one bitof the PN sequence for each successive delay T₁ . . . T_(N). A receivedsignal is applied to the second input of correlator 416.

The delayed code signals and the received signals are mixed at mixers420₀ . . . 420_(N). As is known, when two identical PN sequences aremixed, the output signal has a high average output value. When differentPN sequences or when delayed versions of the same PN sequence are mixed,the output signal has a low average output value. In the system shown inFIG. 4A and FIG. 4B, it must be appreciated that the received signal cancontain the transmitted code signals reflected from a target. The codesignal is delayed by the time it takes for the signals to propagate backand forth from the missile 10 to the target. Thus, the signals at thereceivers contain code signals delayed relative to the signals producedby code operators 406₁ and 406₂. However, if the delays T₁ . . . T_(N)are appropriately selected, the received signal will contain a codesignal with the same delay as one of the outputs of one of the delayelements T₁. . . T_(N). When the output of the delay element with thematching delay is mixed with the received signal at one of the mixers420₁ . . . 420_(N), the mixer will produce a relatively high output. Theoutputs of all the other mixers 420₁ . . . 420_(N) will have loweraverage values.

Filter/detection circuit 415 processes the outputs of mixers 420₀ . . .420_(N) to compute the average value at their outputs. The output ofeach mixer 420₀ . . . 420_(N) is applied to one of the Doppler filters500₀ . . . 500_(N). As can be computed from known signal analysistechniques, the frequency spectrum of the output of each of the mixers420₀ . . . 420_(N) contains the spectrum of the desired signal at abaseband frequency plus various harmonics. Doppler filters 500₀ . . .500_(N) pass the baseband and reject the harmonics. Rectifiers 502₀ . .. 502_(N) and lowpass filters 506₀ . . . 506_(N) compute the averagemagnitude of the output of their respective mixers 420₀ . . . 420_(N).

Filter/detection circuit 415 also contains circuitry to perform otherfunctions. For example, jammer detection circuitry 508 senses the levelof the received signal and indicates the presence of a jammer if thesignal level is too high. Doppler counters 504₁ . . . 504_(N) measurethe frequency, by counting zero crossings, of the received signals. TheDoppler information thus derived gives an indication whether missile 10is in front of or behind the target. The information produced by jammerdetection circuitry 508 and Doppler counters 504₁ . . . 504_(N) is usedby processor 430 (FIG. 4A) in a conventional manner.

Selecting the one of the mixers 420₁ . . . 420_(N) with the largestaverage output value might give an indication of the time it took for asignal to propagate from missile 10 to the target and back. This timecan be easily translated into a range between the missile and target.Processor 430 (FIG. 4A) selects the largest signal from the outputs ofmixers 420₀ . . . 420_(N) after processing by filter/detection 415₁,1and determines range as in prior art systems.

Selecting the mixer with the largest output will produce an erroneousresult if the code signal is not present in the received signal. Forexample, analog processor 412₁,1 compares Code 1 with the signal atantenna R₁. If the target is not illuminated by the Code 1 signaltransmitted by antenna T₁, or the target does not fall within theantenna pattern of antenna R₁, the signal at antenna R₁ will contain theCode 1 signal at such low levels that it can essentially be said to be azero level. In other words, the target may not be in a direction coveredby combined antenna coverage pattern 206₁,1. To determine if a receivedsignal contains the code signal at a high enough level to make theoutput of correlator 416 meaningful, threshold circuit 414 is employed.

Threshold circuit 414 compares the correlated received signal with athreshold signal. Since, as described previously, any signal reflectedfrom a target is delayed relative to the code signal, mixer 420₀ of thecorrelator circuit cannot be mixing a copy of the code signal with thecode signal. The output of mixer 420₀ should thus be a low level signal.This low level signal represents the correlation of the signal withbackground noise and is a background noise reference signal. To say thatthe largest output of correlator 416, after filtering byfilter/detection circuitry 415, represents a signal which reflected froma target, that largest output must exceed the level of the correlationwith background noise by a predetermined level. The selection of thepredetermined level is based on known signal processing techniques.

Threshold circuit 414 determines which of the outputs of mixers 420₀ . .. 420_(N) has a value so large it represents a signal reflected from atarget. Switches 408₁ . . . 408_(N) are normally switched to bypassamplifiers 410₁ . . . 410_(N). The output of each mixer 420₁ . . .420_(N) is, after filtering, passed to one input of comparators 426₁ . .. 426_(N), respectively. The second input to each comparator 426₁ . . .426_(N) is the background noise reference signal derived from mixer420₀. If the average value of any of the outputs of the mixers 420₁ . .. 420_(N) exceeds this reference by the predetermined level, thecorresponding one of the comparators 426₁ . . . 426_(N) will be a logicHI. Otherwise, the output of the comparator will be logic LO. Theoutputs of comparators 426₁ . . . 426_(N) are provided to digital logic432 (FIG. 4A). If a signal transmitted at antenna T₁ is received atantenna R₁, the output of at least one of the comparators 426₁ . . .426_(N) will be a logic HI. Digital logic 432 (FIG. 4A) can then processthe outputs of analog processor 412₁,1 as described below. Conversely,if none of the outputs of comparators 426₁ . . . 426_(N) is logic HI, nofurther processing of the outputs of analog processor 412₁,1 isrequired.

Each of the analog processors 412₁,1, 412₁,2, 412₂,1, and 412₂,2corresponds to one of the combined antenna patterns 206₁,1, 206₁,2,206₂,1, and 206₂,2 in FIG. 3. Analog processor 412₁,1 has as its inputsthe code transmitted by antenna T₁ and the signal received at receiverR₁. Analog processor 412₁,1 thus corresponds to coverage pattern 206₁,1as shown in FIG. 3. Each of the other analog processors corresponds in alike fashion to one of the remaining coverage patterns. A target withincoverage pattern 206₁,1 produces a signal out of correlator 416 whichcauses at least one of the outputs of threshold circuit 414 to be alogic HI.

As shown in FIG. 3, however, there is much overlap in the coveragepatterns 206₁,1, 206₁,2, 206₂,1, and 206₂,2. Thus, the largest output ofthe correlator in more than one of the analog processors 412₁,1, 412₁,2,412₂,1, and 412₂,2 may exceed the corresponding threshold. Processor 430(FIG. 4A) receives the outputs from analog processor 412₁,1, 412₁,2,412₂,1, and 412₂,2 via selection circuits 422₁,1, 422₁,2, 422₂,1, and422₂,2. From these outputs, processor 430 (FIG. 4A) determines which ofthe sectors S₁ . . . S₈ shown in FIG. 3 the target falls.

Processor 430 (FIG. 4A) contains a combination of known analog anddigital processing elements to determine into which of the eight sectorsthe target falls into. Processor 430 contains four selection circuits422₁,1, 422₁,2, 422₂,1, and 422₂,2. Each is connected to the outputs ofa corresponding analog processor 412₁,1, 412₁,2, 412₂,1, and 412₂,2.Taking selection circuit 422₁,1 as representative, it can be seen thatthe selection circuit contains a Greatest of Circuit 424. Greatest-ofcircuit 424 has as its inputs the outputs of the correspondingcorrelator after filtering. The output of greatest-of circuit 424 is thegreatest of the inputs.

The largest value selected by greatest of circuit 424 is converted to adigital word in analog to digital converter 428. This digital word ispassed to digital logic 432. All of the indications from comparators426₁ . . . 426_(N) and the outputs of Doppler counters 504₁ . . .504_(N) are also passed to digital logic 432. It should be noted thatoutputs of Doppler counters 504₁ . . . 504_(N) are used to determinewhen the missile is at the best distance from the target to detonateexplosive charge 14 (FIG. 1). These signals do not play a part indetermining in which direction the energy of the blast should befocused. Also, all of the signals from comparators 426₁ . . . 426_(N)need not be passed to digital logic 432 (FIG. 4A) unless needed forother purposes to implement a directional fuze, it is necessary onlythat a composite signal indicating that one of the outputs ofcomparators 426₁ . . . 426_(N) is a logic HI. If one of outputs is HI,the output of greatest-of circuit 424 is deemed to be a signal reflectedfrom a target rather than merely background noise.

All four selection circuits 422₁,1, 422₁,2, 422₂,1, and 422₂,2 provideto digital logic 432 (FIG. 4A) a digital word representing the level ofthe largest signal selected and a signal indicating whether that signalexceeds the threshold indicating background noise level. Digital logic432 only considers those digital words where the corresponding signalexceeds a threshold as indicated by the outputs of comparators 426₁ . .. 426_(N). From the digital words, digital logic 432 selects the largestdigital word.

The largest digital word gives a coarse estimate of the direction of thetarget relative to missile 10. For example, if the largest digital wordis produced by selection circuit 422₁,2, then the target is in adirection in which coverage pattern 206₁,2 exceeds the other coveragepatterns 206₁,1, 206₂,1, and 206₂,2. This condition is satisfied in allof sector S₃ (FIG. 3) and parts of the adjoining sectors S₂ and S₄ (FIG.3).

To choose between the three possible sectors, digital logic 432 (FIG.4A) performs further processing. Digital logic 432 produces a controlsignal which changes the state of the switches 408₁ . . . 408_(N). Whena switch is closed, the signal at the input of the switch is coupled toone of the amplifiers 410₁ . . . 410_(N). These amplifiers are identicalamplifiers which provide a gain of 7 dB. The selection of a gain of 7 dBcan be understood by reference to FIG. 3. 7 dB is the difference in gainin adjacent ones of the coverage patterns 206₁,1, 206₁,2, 206₂,1, and206₂,2 at the boundaries between the sectors S₁ . . . S₈.

As described above, when the selection circuit associated with coveragepattern 206₁,2 produces the largest digital word, the target could be inthe direction A, B, or C indicated in FIG. 3. When switches 408₁ . . .408_(N) are activated, the received signal associated with coveragepattern 206₁,1 will be amplified 7 dB relative to the other coveragepatterns. This amplification has the effect of increasing coveragepattern 206₁,1 by 7 dB. Thus, at the boundary between sectors S₂ and S₃(FIG. 3), where coverage pattern 206₁,1 had previously been 7 dB lessthan coverage pattern 206₁,2, coverage pattern 206₁,1 will have the sameamplitude as coverage pattern 206₁,2, In all of sector S₂, coveragepattern 206₁,1 will have an amplitude greater than coverage pattern206₁,2. In sector S₃, coverage pattern 206₁,2 will continue to have anamplitude greater than coverage pattern 206₁,1.

Thus, if after switches 408₁ . . . 408_(N) are actuated to includeamplifier 410₁ . . . 410_(N) in the signal path, the largest detectedsignal is associated with coverage pattern 206₁,1 (i.e. the digital wordfrom selection circuit 422₁,1), then the target is in sector S₂.Likewise, if switching the amplifiers in analog processor 412₂,2 intothe signal path causes the largest signal to be associated with coveragepattern 206₂,2, then the target is in sector S₄.

The same technique is applied regardless of in which of the fourcoverage patterns the largest signal falls. In this way, the directionof the target relative to the missile can be assigned to one of eightsectors.

Based on the sector in which the target falls, digital logic 432 selectsappropriate ones of directing charges to detonate. As described above,the directing charges can direct a cloud of shrapnel or increase thevelocity of the shrapnel in a direction centered in one of the eightsectors S₁ . . . S₈. As in a conventional missile, digital logic 432(FIG. 4A) also computes the time to detonate the selected directingcharges and main charge 14.

It should be noted that missile 10 includes a directing charge 16e(FIG. 1) that can create an omni-directional detonation of mainexplosive charge 14. In some instances, such as when the missile is tooclose to the target or when digital logic 432 (FIG. 4A) cannot computethe direction of the target with certainty, directing charge 16e can bedetonated in place of one of the directing charges 16_(a) . . . 16_(d).

Having described one embodiment of the invention, various alternativeembodiments can be constructed. For illustration, FIG. 4 showed somefunctions performed with analog hardware and some functions performedwith digital hardware. One of skill in the art knows that most functionscan be performed with either analog or digital hardware. Also, what isshown as digital logic could be readily implemented as a softwareprogram running on a microprocessor. Also, the preferred embodimentdescribed a velocity focus warhead, but the invention could work withany type of directional warhead.

It is felt, therefore, that this invention should be limited only by thespirit and scope of the appended claims.

What is claimed is:
 1. A missile comprising:a) a first transmit antennaand a second transmit antenna; b) means, coupled to the first-and secondtransmit antennas, for generating a first pseudo noise signal and asecond pseudo noise signal; c) a first receive antenna and a secondreceive antenna; and d) means, coupled to the first and second receiveantennas, for determining the levels of the first and second pseudonoise signals received at the first and second receive antennas.
 2. Themissile of claim 1 wherein the means for determining the levels of thepseudo noise signals comprises means for correlating the signals at thefirst and second receive antennas with the first and second pseudo noisesequences.
 3. The missile of claim 1 additionally comprising means,responsive to the means for determining, for computing the direction ofa target relative to the missile.
 4. The missile of claim 3 additionallycomprising means, coupled to the means for computing the direction of atarget, for selectively firing at least one of a plurality of directingcharges.
 5. The missile of claim 4 wherein the means for computingdirection comprises means for amplifying the signals received at thefirst and second receive antennas by a predetermined amount before thesignals are applied to the means for computing direction.
 6. The missileof claim 2 wherein the means for correlating comprises four correlators,each correlator having two inputs and one output wherein:a) a firstcorrelator has one input coupled to the means for generating the firstpseudo noise sequence and one input coupled to the first receiveantenna; b) the second correlator has one input coupled to the means forgenerating the first pseudo noise sequence and one input coupled to thesecond receive antenna; c) the third correlator has one input coupled tothe means for generating the second pseudo noise sequence and one inputcoupled to the first receive antenna; and d) the fourth correlator hasone input coupled to the means for generating the second pseudo noisesequence and one input coupled to the second receive antenna.
 7. Themissile of claim 6 wherein the outputs of each of the four correlatorsis coupled to digital logic means for selecting the largest signal. 8.The missile of claim 7 wherein the output of each correlator is coupledto the digital logic means through a circuit comprising:a) a switchhaving at least one pole and two throws, the pole being connected to acorrelator and the first throw coupled to an input of the digital logicmeans; and b) an amplifier having an input connected to the second throwand an output coupled to an input of the digital logic means.
 9. Themissile of claim 8 wherein the digital logic means also comprises meansfor selectively actuating the switches and for determining the directionof a target from the largest signal selected before and after theswitches are actuated.
 10. A method of controlling a missile comprisingthe steps of:a) transmitting at least a first pseudo noise signal into afirst region and transmitting a second pseudo noise signal into a secondregion; b) receiving signals from at least a third region and from afourth region; c) comparing the pseudo noise sequences and the receivedsignals to determine the strengths of each pseudo noise signal in eachreceived signal; and d) determining the direction of a target relativeto the missile from the strength of each pseudo noise sequence in eachreceived signal.
 11. The method of controlling a missile of claim 10wherein the step of determining the direction of a target comprises:a)producing a plurality of signals, each signal indicating the level ofone transmitted pseudo noise signal in one received signal; and b)comparing the levels of the plurality of signals.
 12. The method ofcontrolling a missile of claim 11 wherein the step of determining thedirection additionally comprises: assigning a direction based on thedifference between the one of the plurality of signals and a second oneof the plurality of signals.
 13. The method of controlling a missile ofclaim 12 wherein the step of assigning a direction comprises:a)assigning a first direction when the difference between the largest ofthe plurality of signals anti the next largest of the plurality ofsignals exceeds a threshold; and b) assigning a second direction whenthe difference between the largest of the plurality of signals and thenext largest of the plurality of signals is below the threshold.
 14. Themethod of controlling a missile of claim 13 additionally comprising thestep of: directing the force from an explosion in the assigneddirection.
 15. The method of controlling a missile of claim 11 whereinthe step of producing a plurality of signals comprises: correlating eachtransmitted pseudo noise signal with each received signal.
 16. Themethod of controlling a missile of claim 10 additionally comprising thestep of directing a cloud of shrapnel in the direction of the target.17. A method of controlling a missile comprising:a) transmitting atleast:(i) a first transmit signal into a first transmit region aroundthe missile, the first transmit signal being transmitted in differentdirection in the first transmit region with different gains, the patternof gains making a first transmit coverage pattern; (ii) a secondtransmit signal into a second transmit region around the missile, thesecond transmit signal being transmitted in different direction in thesecond transmit region with different gains, the pattern of gains makinga second transmit coverage pattern; b) receiving at least:(i) a firstreceive signal from a first receive region around the missile, the firstreceive signal being received from different directions in the firstreceive region with different gains, the pattern of gains making a firstreceive coverage pattern; (ii) a second receive signal from a secondreceive region around the missile, the second receive region beingreceived from different directions in the second receive region withdifferent gains, the pattern of gains making a second receive coveragepattern; c) determining, by processing the transmitted and receivedsignals, the strengths of signals reflected from objects in at leastfour combined regions, each combined region having a combined coveragepattern with a gain in different directions given by the product of thegain of one transmit coverage pattern and one receive coverage patternand each reflected signal having a strength proportional to the gain ofthe combined coverage in the direction of the object relative to themissile; and d) computing the direction of the object relative to themissile from the determined strength of the reflected signals.
 18. Themethod of claim 17 additionally comprising the step of detonating anexplosive charge and directing the blast from the target in thedirection of the object.
 19. The method of claim 18 wherein the step ofdetermining the strength of reflected signals comprises, for eachcombined region:a) computing the correlation of one transmitted signalwith one received signal; and b) selecting the peak value of thecomputed correlation.
 20. The method of claim 19 wherein the step ofcomputing the direction comprises:a) selecting, from the reflectedsignals from at least four combined regions, the strength of thereflected signal with the largest value and determining the strength ofreflected signals from combined regions adjacent to the combined regionfrom which the largest signal was reflected; b) selecting, as thecomputed direction,(i) the direction in the center of the combinedregion associated with the largest reflected signal when the strength ofthe largest reflected signal exceeds the strength of the reflectedsignals from adjacent combined regions by a predetermined treshold; and(ii) the direction intermediate the center of the combined regionassociated with the largest reflected signal and the center of thecombined region associated with the larger of the reflected signals fromadjacent combined regions when the strength of the largest reflectedsignal does not exceed the strength of the reflected signals fromadjacent combined regions by a predetermined threshold.
 21. The methodof claim 20 wherein the step of selecting the direction comprisesamplifying reflected signals from adjacent combined regions by thepredetermined threshold.